Polyethylene (PE) and isotactic polypropylene (iPP) are the two most widely produced polymers in the world, accounting for over half of the approximately 280 million tons of plastic produced in 2012. These semicrystalline polyolefins are ubiquitous because of their low cost and impressive physical and thermal properties, allowing for their use in a wide array of applications. Since the discovery of these materials in the 1950's, relatively few new classes of semicrystalline polymers have been commercialized, and even fewer where the monomers are nearly as readily available and inexpensive as ethylene and propylene.
Stereocomplexation occurs when a stereoselective interaction between two stereoregular complementary polymers in the crystalline state results in altered physical and thermal properties in comparison to the parent polymers. Most commonly, stereocomplexes are formed between enantiomerically complementary polymer strands. Stereocomplexation improves and allows for tunability of polymer properties, including crystallinity as well as biodegradability.
Epoxides have been studied in alternating copolymerizations with CO2 to form polycarbonates and with cyclic anhydrides to form polyesters. In the case of propylene oxide (PO)/CO2 copolymerization, even highly regio- and stereoregular polycarbonates are amorphous. However, the copolymerization of PO with cyclic anhydrides has resulted in the formation of a new class of semicrystalline polyesters. Many currently available aliphatic polyesters, including polylactic acid (PLA), and polyhydroxybutyrate (PHB), can be safely decomposed in aerobic composting environments, anaerobic landfill environments, and in vivo in the case of biomedical devices. However, commercializing many current biodegradable polyesters challenges the existing industrial infrastructure because the processes required to produce them rely partially or fully on biotechnology.